The present invention relates to optically active cephalosporin analogs and, more particularly, it pertains to optically active compounds of cephalosporin analogs represented by the general formula (I) ##STR1## wherein R.sub.1 represents a hydrogen, a lower alkyl group or a lower acyl group, R.sub.2 represents a hydrogen or a protective group of carboxylic acid, and the hydrogens at the 6- and 7-positions have cis configuration, the salts thereof and processes for producing the same.
Heretofore, a carbacephem compound, which is named according to the nomenclature in J. Am. Chem. Soc. 96, 7584 (1974), wherein the sulfur atom of cephalosproin is substituted with a carbon atom and which has a substituted methyl group at the 3-position is described in the above reference and J. Med. Chem. 20, 551 (1977). However, no compound of this type having especially strong antibacterial activity has been reported.
The present inventors have succeeded in preparing carbacephem compounds having various substituents at the 4-, 5- and 3-positions [The numbering system is as shown in general formula (I)]. The compounds are described in the specifications of Japanese Published Unexamined Patent Application No. 128591/79, German Offenelegungsschrift No. 2911786, referred to as "G.O." hereinafter, and U.S. Patent Application Ser. No. 23,645 filed on Mar. 23, 1979.
Further, the present inventors have succeeded in preparing novel acylated carbacephems which are new antibiotics having strong antibacterial activities. These are described in Japanese Published Unexamined Patent Application No. 128591/79, G.O. 2911787 and U.S. Patent Application Ser. No. 23,646 filed on Mar. 23, 1979.
However, cephalosporin analogs mentioned above are prepared by synthetic methods using optically inactive starting compounds, and they are optically inactive dl [represented by (.+-.)] compounds unless they have optically active acyl group. More specifically, compounds represented by the general formula (II) ##STR2## wherein R.sub.2 has the same significance as defined above, R.sub.3 represents a hydrogen, a lower alkyl group or a lower acyloxy group and the hydrogen atoms at the 6- and 7-positions have cis configuration are present as a mixture of equal amounts of the mirror image compounds represented by the formulae (II-1) and (II-2) ##STR3## wherein R.sub.2 and R.sub.3 have the same significance as defined above.
As a result of various studies, the present inventors have succeeded in preparing and isolating one of the optically active mirror image compounds represented by the assumed formula (II-1), which is disclosed in Japanese Patent Application No. 14533/79 (European Patent Application 80100663.6)
Similarly, compounds represented by the general formula (I) wherein the hydrogen atoms at the 6- and 7-positions have cis configuration are also present as a mixture of equal amounts of the mirror image compounds represented by the formulae (I-1) and (I-2) ##STR4## wherein R.sub.1 and R.sub.2 have the same significance as defined above.
As a result of further studies, the present inventors have also succeeded in preparing and isolating one of the optically active mirror image compounds represented by the formula (I-1).